People often describe Safin's strokes as heavy and I would hardly say he uses "lots of spin". To me, a heavy ball is produced when someone uses good technique and utilizes mass to hit a ball solidly, rather than having flashy, whippy strokes that produce tons of topspin. Federer's shots are heavy, and also use spin, but I don't believe it is spin that classifies a stroke as heavy. Safin's backhand is what I would call "heavy".
I disagree with TennsDog in other words.